1. Field of the Invention
The present invention relates to polycarbonate containers and more particularly relates to polycarbonate containers having an amorphous nylon intermediate layer.
2. Description of Related Art
Multilayer hollow polycarbonate containers having intermediate layers comprised of a thermoplastic resin exhibiting gas-barrier properties are known in the art. For example, Collins, U.S. Pat. No. 4,513,037 sets forth a multilayered hollow polycarbonate container comprised of (i) at least one, inner polycarbonate layer; (ii) at least one outer polycarbonate layer; and (iii) at least one intermediate layer between said inner polycarbonate layer and said outer polycarbonate layer comprised of a thermoplastic resin exhibiting gas-barrier properties. Various resins are set forth as being suitable for coextrusion blow molding and include polyesters, nylons, polyvinylchloride, polyvinyldiene chloride, polyvinylalcohol, acrylonitrile, and copolymers of ethylene and vinyl alcohol such as those made by hydrolizing a copolymer of vinylacetate and ethylene. These multilayer polycarbonate containers offer several advantages over comparable monolayer polycarbonate containers including the ability to keep out oxygen from juices and other perishable foods therein, thereby preventing these foods from spoilage for longer periods of time than simple monolayer polycarbonate containers. These multilayered hollow polycarbonate containers also have several advantages over comparable glass containers including lighter weight and greater impact strength and resistance to breakage.
However, these multilayered polycarbonate containers typically have one or more of the following problems associated with them; (i) the apparent melt viscosities of the various layers differ significantly at extrusion temperatures thereby making it difficult to coextrusion blow mold bottles therefrom; (ii) regrind blends made from the waste materials obtained during blow molding typically lack clarity thereby making them useless as an internal layer for clear multilayered bottles; or (iii) the resin employed in the intermediate layer typically lacks a glass transition temperature sufficiently high to provide shape retention of the container during hot fill of juices usually in excess of 82.degree. C., therein. Thus for example, crystalline polyamides while generally being suitable as an intermediate layer for multilayered polycarbonate containers suffer from several problems including lacking clarity and being somewhat difficult to coextrude with polycarbonate due to melt viscosity differences between aromatic polycarbonates and crystalline polyamides, and producing an opaque resin when blended with polycarbonate.
It is therefore an object of the present invention to provide multilayered polycarbonate containers having resin layers which have similar melt viscosities at extrusion temperatures for improved processability during coextrusion blow molding thereof.
It is a further object to provide a clear polycarbonate container employing resin layers which when made into a regrind blend provide a clear resin blend for use as an additional intermediate layer in the container.
Additionally, it is an object of the present invention to provide an intermediate layer having excellent gas barrier properties.